Turned down by umpire and exploited (7)
I believe the answer is:
refused
'turned down' is the definition.
('refuse' can be a synonym of 'turn down')
'umpire and exploited' is the wordplay.
'umpire' becomes 'ref' (short for referee).
'and' means one lot of letters go next to another.
'exploited' becomes 'used' (synonyms).
'ref'+'used'='REFUSED'
'by' is the link.
(Other definitions for refused that I've seen before include "Was unwilling to accept" , "Not accepted" , "Said no (7)" , "Declined, rejected" , "turned down appeal" .)